archvillainetteandClaude Fable 5
da59e54261
Implement Backend interface with Probe/Get/Put methods, ProbeState constants, and LocalBackend using filesystem storage with atomic operations and hash verification. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
114 lines
2.4 KiB
Go
114 lines
2.4 KiB
Go
package depot
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import (
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"context"
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"crypto/sha256"
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"fmt"
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"io"
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"os"
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"path/filepath"
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)
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// LocalBackend implements Backend for local filesystem storage.
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type LocalBackend struct {
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Root string
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}
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// Name returns the backend name.
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func (b *LocalBackend) Name() string {
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return "local"
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}
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// Probe checks if a blob exists.
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func (b *LocalBackend) Probe(ctx context.Context, sha string) (ProbeState, bool, error) {
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blobPath := filepath.Join(b.Root, BlobKey(sha))
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_, err := os.Stat(blobPath)
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if err == nil {
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return Present, false, nil
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}
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if os.IsNotExist(err) {
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return Absent, false, nil
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}
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// Real I/O error (permission, etc.)
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return Absent, false, err
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}
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// Put copies the file from src to the blob storage.
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func (b *LocalBackend) Put(ctx context.Context, sha, src string) error {
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blobPath := filepath.Join(b.Root, BlobKey(sha))
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blobDir := filepath.Dir(blobPath)
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// Create parent directories
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if err := os.MkdirAll(blobDir, 0755); err != nil {
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return err
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}
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// Create temp file in the same directory for atomic rename
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tmpFile, err := os.CreateTemp(blobDir, ".tmp-")
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if err != nil {
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return err
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}
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defer os.Remove(tmpFile.Name())
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// Copy source to temp file
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srcFile, err := os.Open(src)
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if err != nil {
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tmpFile.Close()
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return err
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}
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defer srcFile.Close()
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_, err = io.Copy(tmpFile, srcFile)
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tmpFile.Close()
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if err != nil {
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return err
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}
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// Atomic rename
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return os.Rename(tmpFile.Name(), blobPath)
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}
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// Get fetches the blob, re-hashes it, and deletes it if the hash doesn't match.
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func (b *LocalBackend) Get(ctx context.Context, sha, dest string) error {
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blobPath := filepath.Join(b.Root, BlobKey(sha))
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// Create temp file in dest directory for atomic rename
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destDir := filepath.Dir(dest)
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if err := os.MkdirAll(destDir, 0755); err != nil {
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return err
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}
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tmpFile, err := os.CreateTemp(destDir, ".tmp-")
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if err != nil {
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return err
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}
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defer os.Remove(tmpFile.Name())
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// Copy and hash simultaneously
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srcFile, err := os.Open(blobPath)
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if err != nil {
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tmpFile.Close()
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return err
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}
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defer srcFile.Close()
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hasher := sha256.New()
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teeReader := io.TeeReader(srcFile, hasher)
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_, err = io.Copy(tmpFile, teeReader)
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tmpFile.Close()
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if err != nil {
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return err
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}
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// Check hash
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gotHash := fmt.Sprintf("%x", hasher.Sum(nil))
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if gotHash != sha {
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os.Remove(tmpFile.Name())
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return fmt.Errorf("hash mismatch: expected %s, got %s", sha, gotHash)
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}
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// Atomic rename
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return os.Rename(tmpFile.Name(), dest)
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}
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